U.S. patent application number 12/679933 was filed with the patent office on 2010-08-05 for vinyl alcohol polymer-containing coating agent for paper and paper and thermal paper coated with the coating agent.
This patent application is currently assigned to KURARAY CO., LTD.. Invention is credited to Koji Hori, Atsushi Jikihara, Kazuki Nakagawa, Masato Nakamae, Misa Watanabe.
Application Number | 20100196731 12/679933 |
Document ID | / |
Family ID | 40511243 |
Filed Date | 2010-08-05 |
United States Patent
Application |
20100196731 |
Kind Code |
A1 |
Jikihara; Atsushi ; et
al. |
August 5, 2010 |
VINYL ALCOHOL POLYMER-CONTAINING COATING AGENT FOR PAPER AND PAPER
AND THERMAL PAPER COATED WITH THE COATING AGENT
Abstract
A vinyl alcohol polymer-containing coating agent for paper is
provided that allows a curing step to be omitted after a paper
surface is coated therewith and makes it possible to form a layer
(for example, a coating layer or a color developing layer) that is
excellent in water resistance and is subjected to less yellowing
over time. It is an aqueous composition containing a vinyl alcohol
polymer (A) in which the content X of vinyl alcohol units (mol %)
and the content Y of ethylene units (mol %) satisfy a formula
X+0.2Y>95, where X<99.9 and 0.ltoreq.Y.ltoreq.10, and an
addition condensate (B) between ethylene urea and glyoxal in which
the content of terminal aldehyde groups per gram of solid content
is 1.2 to 3.0 (mmol), wherein the solid content weight ratio
between the vinyl alcohol polymer (A) and the addition condensate
(B) is in a range of (A):(B)=99:1 to 50:50.
Inventors: |
Jikihara; Atsushi; (Okayama,
JP) ; Nakamae; Masato; (Okayama, JP) ;
Nakagawa; Kazuki; (Wakayama, JP) ; Hori; Koji;
(Wakayama, JP) ; Watanabe; Misa; (Wakayama,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, L.L.P.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
KURARAY CO., LTD.
Kurashiki-shi, Okayama
JP
|
Family ID: |
40511243 |
Appl. No.: |
12/679933 |
Filed: |
September 19, 2008 |
PCT Filed: |
September 19, 2008 |
PCT NO: |
PCT/JP08/66979 |
371 Date: |
March 25, 2010 |
Current U.S.
Class: |
428/511 ;
524/555 |
Current CPC
Class: |
B41M 5/3372 20130101;
B41M 5/5254 20130101; B41M 5/44 20130101; D21H 19/24 20130101; D21H
19/20 20130101; Y10T 428/31895 20150401 |
Class at
Publication: |
428/511 ;
524/555 |
International
Class: |
B32B 27/10 20060101
B32B027/10; C08L 29/04 20060101 C08L029/04 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 27, 2007 |
JP |
2007-252553 |
Claims
1. A coating agent for paper comprising: a vinyl alcohol polymer
(A) in which the content X of a vinyl alcohol unit (mol %) and the
content Y of an ethylene unit (mol %) satisfy the following formula
(1): X+0.2Y>95 (1) where X<99.9 and 0.ltoreq.Y<10; and an
addition condensate (B) between ethylene urea and glyoxal in which
the content of a terminal aldehyde group per gram of solid content
is 1.2 to 3.0 (mmol), wherein the solid content weight ratio
between the vinyl alcohol polymer (A) and the addition condensate
(B) is in a range of (A):(B)=99:1 to 50:50.
2. The coating agent for paper according to claim 1, wherein the
vinyl alcohol polymer (A) satisfies the following formula (2) with
respect to the contents X and Y: X+0.2Y>98.5 (2) where X<99.9
and 0.ltoreq.Y<10.
3. The coating agent for paper according to claim 1, wherein the
vinyl alcohol polymer (A) contains an ethylene unit.
4. Paper having a surface coated with a coating agent for paper
according to claim 1.
5. Thermal paper having a surface coated with a coating agent for
paper according to claim 1.
Description
TECHNICAL FIELD
[0001] The present invention relates to a coating agent for paper
containing a vinyl alcohol polymer as well as paper and thermal
paper coated with the coating agent.
BACKGROUND ART
[0002] A vinyl alcohol polymer (hereinafter also referred to simply
as a "PVA") has performances unsurpassed by other water-soluble
resins in terms of its film-forming properties and adhesiveness
(for example, adhesion strength). Thus, it is used widely for
various binders, adhesives, or surface treatment agents. One of the
applications of the PVA is a coating agent for paper aimed at, for
example, improving paper surface strength. Paper having a PVA
coated surface is used as, for example, printing paper. The PVA
contains modified polyvinyl alcohol having a constituent unit other
than a vinyl alcohol unit, for example, an ethylene unit.
[0003] There are various types of paper printing methods. The
current mainstream method is offset printing. In offset printing, a
nonimage area and an image area are formed in a metal plate, and
dampening water and ink are placed on the nonimage area and the
image area, respectively. Thereafter, these are transferred by
contact to a rubber blanket and further are transferred from the
blanket to a paper surface to form an image. Therefore, printing
paper that is used for offset printing is required to have water
resistance to dampening water. The PVA itself, however, is water
soluble and is poor in water resistance. Accordingly, a coating
agent formed of a combination of a PVA and a crosslinker (a water
resistant agent) is used in general.
[0004] The PVA is also used for a coating layer (an overcoat layer
or a backcoat layer) of a thermal recording material such as
thermal paper, or a binder of a color developing layer (a pigment
layer or a dye layer) based on its excellent film-forming
properties and adhesiveness. Generally, a leuco dye is often used
as a coloring source for the thermal recording material. However,
such a recording material has poor stability of recorded images.
For example, contacts between the thermal recording surface and
fats or a plasticizer contained in a plastic film cause color
fading of the images or discoloring of the ground part (the
nonimage area). The coating layer has effects of preventing such
color fading and discoloring and improving the stability of images.
Generally, a PVA modified by a carboxyl group is used for the
coating layer. However, the carboxyl group-modified PVA tends to
dissolve in water. Thus, it is necessary that the PVA is combined
with a crosslinker to form a coating agent, and that thermal paper
is coated with the coating agent, dried, and subjected to a curing
step. The curing step is a step for allowing a formed coating layer
to attain a desired waterproof level by storing the paper coated
with the coating agent under an environment of 30 to 40.degree. C.
for a period of about one day to one week. In order to carry out
the curing step, a storage place with a large area is required, and
the curing step is a major factor in reducing the production
efficiency of the thermal recording material. Accordingly, there is
a need for a coating agent that allows the curing step to be
omitted.
[0005] In order to improve this disadvantage, i.e. poor water
resistance, of the PVA, various methods have been studied until
now.
[0006] A method of combining a PVA and glyoxal to be used as a
crosslinker to form a coating layer on printing paper has been
known widely. In this method, the PVA can be cross-linked at a
comparatively low temperature and the resultant coating layer can
be provided with water resistance. However, this method has a
disadvantage in that the coating layer turns yellow over time.
[0007] JP 8-269289 A discloses a water resistant composition
containing an ethylene-modified PVA, a chitosan compound, and a
polyaldehyde compound. However, in the case of the composition
disclosed in JP 8-269289 A, a chitosan compound and a polyaldehyde
compound are used as water resistant agents. Therefore, when
exposed to the air for a long time, a layer formed of the
composition turns yellow, which is a disadvantage. JP9-66666 A
discloses a recording material in which a crosslinker and an
ethylene-modified PVA with a specific constitution (with a
syndiotacticity of at least 55 mol % in terms of syndiotactic diad
content and a degree of saponification of at least 85 mol %) are
used as a binder of a color developing layer. JP 11-208115 A
discloses a thermal recording material in which an
ethylene-modified PVA and a compound containing at least two
aziridine groups to be used as a crosslinker are used for an
overcoat layer. However, the combination of the ethylene-modified
PVA and the crosslinker disclosed in each of JP 9-66666 A and JP
11-208115 A cannot always provide sufficient water resistance.
DISCLOSURE OF INVENTION
[0008] With these problems in mind, the present invention is
intended to provide a coating agent for paper that is a vinyl
alcohol polymer-containing coating agent for paper, that allows a
curing step to be omitted after a paper surface is coated
therewith, and that makes it possible to form a layer (for example,
a coating layer or a color developing layer) that is excellent in
water resistance and is subjected to less yellowing over time.
[0009] As a result of dedicated studies, the present inventors
found that a PVA and a crosslinker allowed to have specific
compositions made it possible to obtain such a coating agent for
paper.
[0010] That is, the coating agent for paper of the present
invention contains; a vinyl alcohol polymer (A) in which the
content X of vinyl alcohol units (mol %) and the content Y of
ethylene units (mol %) satisfy the following formula (1):
X+0.2Y>95 (1)
where X<99.9 and 0.ltoreq.Y<10; and an addition condensate
(B) between ethylene urea and glyoxal in which the content of
terminal aldehyde groups per gram of solid content is 1.2 to 3.0
(mmol), wherein the solid content weight ratio between the vinyl
alcohol polymer (A) and the addition condensate (B) is in a range
of (A):(B)=99:1 to 50:50.
[0011] Paper of the present invention is paper whose surface is
coated with the above-mentioned coating agent for paper of the
present invention.
[0012] Thermal paper of the present invention is thermal paper
whose surface is coated with the above-mentioned coating agent for
paper of the present invention.
[0013] According to the present invention, since the coating agent
for paper contains a PVA (A), in which the content X of vinyl
alcohol units and the content Y of ethylene units are in the
specific ranges, and an addition condensate (B) between ethylene
urea and glyoxal, in which the content of terminal aldehyde groups
is in a specific range, the coating agent for paper can be obtained
that allows a curing step to be omitted after a paper surface is
coated therewith and that makes it possible to form a layer (for
example, a coating layer or a color developing layer) that is
excellent in water resistance and is subjected to less yellowing
over time.
[0014] The paper and thermal paper of the present invention are
those with surfaces coated with the aforementioned coating agent
for paper of the present invention and can be produced, for
example, with the curing step being omitted that is conventionally
required for improving water resistance of the layer (for example,
a coating layer or a color developing layer) formed by application
of a coating agent. Furthermore, the paper and thermal paper each
can have a layer (for example, a coating layer or a color
developing layer) that is excellent in water resistance and is
subjected to less yellowing over time. That is, the paper and
thermal paper of the present invention are excellent in, for
example, water resistance, image record retention properties,
plasticizer resistance, and productivity, and can be used suitably
for various printing methods including offset printing and thermal
printing.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] Hereinafter, the layer that is formed by application of a
coating agent for paper to a paper surface is referred to simply as
a "layer". Examples of this layer include the aforementioned
coating layer and color developing layer (in the color developing
layer, generally, the coating agent for paper serves as a binder of
a pigment or dye). However, the layer is not particularly limited
to these two types of layers.
[PVA (A)]
[0016] The PVA (A) is not particularly limited as long as it is a
polyvinyl alcohol polymer that satisfies the following formula
(1):
X+0.2Y>95 (1),
where X denotes the content (mol %) of vinyl alcohol units in the
PVA (A) and Y denotes the content (mol %) of ethylene units in the
PVA (A). X and Y are numerical values that satisfy formulae
X<99.9 and 0.ltoreq.Y<10, respectively.
[0017] The content X of vinyl alcohol units in the PVA (A) (this
also can be referred to as the degree of saponification of the PVA
(A)) is required to be less than 99.9 mol % and is preferably 99.8
mol % or less and further preferably 99.7 mol % or less. When the
content X is 99.9 mol % or more, the viscosity stability of the
coating agent is deteriorated and a practical coating agent cannot
be obtained. Furthermore, the content X is preferably 95 mol % or
more, more preferably 98.5 mol % or more, and further preferably 99
mol % or more. That is, the content X is preferably at least 95 mol
% but less than 99.9 mol %, more preferably 98.5 to 99.8 mol %, and
further preferably 99 to 99.7 mol %. When the content X is in these
ranges, a layer that is further excellent in water resistance can
be formed.
[0018] The PVA (A) has ethylene units, that is, it is preferable
that the content Y of the ethylene units in the PVA (A) exceed 0
mol % (for example, 0<Y<10). In this case, a layer that is
further excellent in water resistance can be formed.
[0019] The content Y of the ethylene units in the PVA (A) is
required to be less than 10 mol % and is preferably 1 to 9 mol %
and more preferably 3 to 8 mol %. When the content Y is 10 mol % or
more, water solubility of the PVA (A) is added and thereby it is
difficult to form the coating agent and the viscosity stability of
the coating agent may be deteriorated.
[0020] The content Y in the PVA (A) can be determined by a known
method. For example, it may be determined by carrying out
.sup.1H-NMR (proton nuclear magnetic resonance) measurement with
respect to a vinyl ester polymer, which is a precursor of the PVA.
A specific example follows. Purification by reprecipitation is
carried out at least three times using an n-hexane/acetone mixed
solution with respect to a vinyl ester polymer, which is a
measuring object. Next, the polymer thus purified is dried under
reduced pressure at 80.degree. C. for three days. Subsequently, the
well dried polymer is dissolved in DMSO-d.sub.6 (deuterated
dimethyl sulfoxide) and .sup.1H-NMR is performed to the polymer at
80.degree. C. The content Y can be determined from the peak (with a
chemical shift of 4.7 to 5.2 ppm) derived from methine that is
present in the main chain of the vinyl ester unit and the peak
(with a chemical shift of 0.8 to 1.6 ppm) derived from methylene
that is present in the main chains of the vinyl ester unit and
ethylene unit in the measured profile.
[0021] Preferably, the PVA (A) satisfies the following formula (2)
with respect to the above-mentioned contents X and Y, because in
this case a layer can be formed that is further excellent in water
resistance and that further is prevented from yellowing over
time:
X+0.2Y>98.5 (2)
where X and Y are numerical values that satisfy formulae X<99.9
and 0.ltoreq.Y<10, respectively.
[0022] Generally, the PVA (A) can be obtained by polymerizing vinyl
ester monomers, such as vinyl acetate, individually or together
with ethylene by a known polymerization method (for example, bulk
polymerization, solution polymerization using a solvent such as
methanol, emulsion polymerization, or suspension polymerization),
and then saponifying the resultant polymer by various
saponification methods (for example, alkali saponification, acid
saponification, or alcoholysis). The vinyl ester monomers that can
be used in addition to the aforementioned vinyl acetate include
various monomers such as vinyl formate, vinyl propionate, vinyl
valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl
benzoate, vinyl versatate, and vinyl pivalate, but it is preferable
that vinyl acetate be used.
[0023] The degree of polymerization (determined by viscosity
average molecular weight) of the PVA (A) is not particularly
limited but generally is about 200 to 4000, preferably about 250 to
3000, and particularly preferably about 300 to 2000. When the
degree of polymerization of the PVA is lower than 200, a layer with
sufficient water resistance and plasticizer resistance may not be
formed. On the other hand, when the degree of polymerization of the
PVA exceeds 4000, the viscosity of the coating agent may increase
excessively and the coating properties thereof may deteriorate. The
degree of polymerization of the PVA (A) can be evaluated based on
the provision of JIS-K6726 (The test methods for polyvinyl
alcohol).
[0024] The PVA (A) may contain a constituent unit derived from a
monomer that can be copolymerized with the vinyl ester monomer and
ethylene within the range where the effects of the present
invention are not impaired. Examples of such a monomer include
alpha-olefins such as propylene, 1-butene, isobutene, and 1-hexene;
vinyl ethers such as methyl vinyl ether, ethyl vinyl ether,
n-propyl vinyl ether, i-propyl vinyl ether, and n-butyl vinyl
ether; hydroxyl group-containing vinyl ethers such as ethylene
glycol vinyl ether, 1,3-propanediol vinyl ether, and 1,4-butanediol
vinyl ether; allyl acetate; allyl ethers such as propyl allyl
ether, butyl allyl ether, and hexyl allyl ether; monomers
containing an oxyalkylene group; vinyl silanes such as
vinyltrimethoxysilane; isopropenyl acetate; hydroxyl
group-containing alpha-olefins such as 3-buten-1-ol, 4-penten-1-ol,
5-hexen-1-ol, 7-octen-1-ol, 9-decen-1-ol, and
3-methyl-3-buten-1-ol; carboxyl group-containing monomers such as
fumaric acid, maleic acid, itaconic acid, maleic anhydride, and
itaconic anhydride; sulfonic acid group-containing monomers such as
ethylenesulfonic acid, allylsulfonic acid, methallylsulfonic acid,
and 2-acrylamide-2-methylpropanesulfonic acid; cationic
group-containing monomers such as vinyloxyethyltrimethylammonium
chloride, vinyloxybutyltrimethylammonium chloride,
vinyloxyethyldimethylamine, vinyloxymethyldiethylamine,
N-acrylamidemethyltrimethylammonium chloride,
3-(N-methacrylamide)propyltrimethylammonium chloride,
N-acrylamideethyltrimethylammonium chloride,
N-acrylamidedimethylamine, allyltrimethylammonium chloride,
methallyltrimethylammonium chloride, dimethylallylamine, and
allylethylamine; acrylic acid, acrylic acid ester, acrylamide, and
acrylamide derivatives. The amount of modification of the PVA (A)
by a constituent unit derived from such a monomer is not
particularly limited as long as the effects of the present
invention are not impaired. Generally, however, it is 20 mol % or
less and preferably 10 mol % or less, with respect to all the
constituent units of the PVA (A).
[0025] The PVA (A) may be a terminal modified PVA obtained by the
aforementioned polymerization and saponification that are carried
out in the presence of a thiol compound such as thiol acetic acid,
mercaptopropionic acid, or dodecylmercaptan.
[0026] The PVA (A) may be a modified PVA obtained by saponifying a
polymer obtained by polymerizing vinyl ester monomers individually
or together with ethylene and then further modifying it by the
post-reaction, as long as the effects of the present invention are
not impaired. Examples of such a modified PVA include various
acetalized PVAs that are modified with aldehyde such as
butylaldehyde, and acetoacetyl group-modified PVAs into which an
acetoacetyl group has been introduced by using, for example,
diketene. When the PVA (A) is a modified PVA, it is preferably an
acetoacetyl group-modified PVA, that is, a PVA containing a
constituent unit having an acetoacetyl group.
[0027] The amount of modification in the acetoacetyl group-modified
PVA, that is, the content of the constituent units having
acetoacetyl groups in this modified PVA, is preferably 8 mol % or
less in general and more preferably 7 mol % or less. An excessively
large amount of modification may deteriorate viscosity stability of
the coating agent.
[Addition Condensate (B)]
[0028] In the addition condensate (B) between ethylene urea and
glyoxal, the content of the terminal aldehyde groups per gram of
solid content is 1.2 to 3.0 (mmol: millimole). Hereinafter, the
unit of the content of the terminal aldehyde groups per gram of
solid content is indicated as (mmol/g-solid content).
[0029] The addition condensate (B) can be obtained by various
production methods. For example, ethylene urea and glyoxal are
mixed in a range of ethylene urea glyoxal=1:0.9 to 1.5 in terms of
a molar ratio. Then, pH of the reaction system is adjusted, and an
addition condensation reaction is allowed to proceed at a
predetermined temperature to form the addition condensate (B).
[0030] The mixing ratio of ethylene urea and glyoxal that is used
in obtaining the addition condensate (B) is preferably 0.9 to 1
mole of glyoxal to 1 mole of ethylene urea.
[0031] When the mixing ratio of ethylene urea and glyoxal is
ethylene urea glyoxal=1 mole:more than 1.5 mole, it becomes highly
probable that both terminals of the resultant addition condensate
are aldehyde groups and thereby the viscosity stability of the
coating agent deteriorates. Furthermore, in this case, an amount of
glyoxal is excessive to ethylene urea, and this increases the
amount of residual glyoxal remaining in the addition condensate and
deteriorates the safety of the coating agent. The volatility of
glyoxal is not as high as that of formaldehyde, which also is an
aldehyde compound, but glyoxal has irritating properties with
respect to the skin and mucosa of the human body and the
mutagenicity thereof is positive. Therefore, from the safety
viewpoint, a small amount of residual glyoxal is desired.
[0032] On the other hand, when the mixing ratio of ethylene urea
and glyoxal is ethylene urea:glyoxal=1 mole:less than 0.9 mole, the
amount of residual glyoxal in the addition condensate is reduced
and thereby the safety of the coating agent is improved. However,
it becomes highly probable that both terminals of the resultant
addition condensate are amide groups, and thus water resistance of
the resultant layer is deteriorated.
[0033] The content of the terminal aldehyde groups in the addition
condensate (B) can be evaluated by the method described in JP
59-163497 A (U.S. Pat. No. 4,471,087) as shown in Examples. The
content of the terminal aldehyde groups in the addition condensate
(B) is preferably 1.5 to 2.4 (mmollg-solid content).
[0034] The amount of the residual glyoxal in the addition
condensate (B) is generally 0.3 wt % or less in a solution in which
the solid content concentration of the addition condensate (B) is
40 wt %.
[0035] Judging from the mutagenicity data of individual glyoxal
described in "Mutagenicity test data of existing chemical
substances" (issued by Japan Chemical Industry Ecology-Toxicology
& Information Center, 1996), when the amount of the residual
glyoxal in the addition condensate (B) is in the above-mentioned
range, the mutagenicity derived from the residual glyoxal is
negative.
[0036] Various conditions of the reaction system of the additional
condensation between ethylene urea and glyoxal are not particularly
limited. However, the temperature (reaction temperature) of the
system is preferably 40 to 70.degree. C. When the reaction
temperature is lower than 40.degree. C., the velocity of the
reaction between both becomes excessively slow and the amount of
residual glyoxal in the resultant addition condensate increases. On
the other hand, when the reaction temperature exceeds 70.degree.
C., the coloring of the resultant addition condensate increases and
the stability thereof is deteriorated.
[0037] Furthermore, for example, pH of the reaction system in which
the addition condensation is carried out is preferably 4 to 7. When
the pH of the system is lower than 4, the reaction of the addition
condensation proceeds excessively, and thereby the stability of the
resultant addition condensate is deteriorated. On the other hand,
when the pH of the system exceeds 7, coloring of the resultant
addition condensate increases and the stability thereof is
deteriorated. The pH of the system in which the addition
condensation is carried out can be adjusted with a pH adjuster. The
pH adjuster is not particularly limited, and for example, sodium
hydroxide, potassium hydroxide, sodium carbonate, ammonium
carbonate, potassium carbonate, sodium phosphate, sodium hydrogen
phosphate, ammonium phosphate, or ammonium hydrogen phosphate.
[0038] The addition condensate (B) is obtained as an aqueous
solution through the above-mentioned reaction. It is preferable
that ethylene urea and glyoxal be subjected to addition
condensation in such a manner that the solid content concentration
in the aqueous solution is 10 to 60 wt %. When the concentration
exceeds 60 wt %, the viscosity of the resultant aqueous solution is
high, and therefore the property of mixing with other materials is
deteriorated and the stability thereof also is deteriorated. On the
other hand, if the concentration is lower than 10 wt %, it takes
time to form a layer when it is used as a coating agent. It is
preferable that both be subjected to addition condensation in such
a manner that the solid content concentration is 15 to 50 wt %.
[0039] The addition condensate (B) may be obtained as follows.
Ethylene urea and glyoxal are mixed together in the range of
ethylene urea:glyoxal=1:0.9 to 1 in terms of molar ratio, and after
pH of the system in which addition condensation is carried out is
adjusted to 4 to 7 with a pH adjuster, the reaction is allowed to
proceed at 40 to 60.degree. C.
[Coating Agent for Paper]
[0040] The coating agent of the present invention contains the
aforementioned PVA (A) and addition condensate (B) in the range of
(A):(B)=99:1 to 50:50 in terms of solid content weight ratio. Since
a layer can be formed that is further excellent in water resistance
and that is subjected to further less yellowing over time, the
weight ratio is preferably in the range of (A):(B)=98:2 to 60:40
and more preferably (A):(B)=97:3 to 65:35. When the solid content
weight ratio of the addition condensate (B) is lower than the case
of (A):(B)=99:1, the addition condensate (B) does not provide a
sufficient effect as a crosslinker, and thereby a layer with
sufficient water resistance is not formed. On the other hand, when
the solid content weight ratio of the addition condensate (B) is
higher than (A):(B)=50:50, the viscosity stability of the coating
agent is deteriorated.
[0041] The coating agent of the present invention may contain
various additives as required. Examples of the additives include
water resistant agents such as polyvalent metal salt and water
soluble polyamide resin; plasticizers such as glycols and glycerol;
pH regulators such as ammonia, sodium hydroxide, sodium carbonate,
and phosphoric acid; and antifoaming agents, mold release agents,
and surfactants. As described above, however, in order to improve
the safety of the coating agent, it is preferable that glyoxal as
well as urea resin and melamine resin that may volatilize
formaldehyde in use be not contained as additives.
[0042] The coating agent of the present invention also may contain
the following additives in the range where the effects of the
present invention are not impaired: for example, water soluble
polymers such as starch, modified starch, casein, and
carboxymethylcellulose; and synthetic resin emulsions such as
styrene-butadiene latex, polyacrylic acid ester emulsion, vinyl
acetate-ethylene copolymer emulsion, and vinyl acetate-acrylic acid
ester copolymer emulsion.
[0043] The coating agent of the present invention can be used as,
for example, a clear coating agent or a color developer (a pigment
or a dye) coating agent. When the coating agent of the present
invention is used as a clear coating agent, for example, the
aforementioned coating layer can be formed on a paper surface. When
it is used as a color developer coating agent, for example, the
aforementioned color developing layer can be formed on a paper
surface. The amount of the coating agent of the present invention
to be used is not particularly limited and generally is about 0.1
to 30 g/m.sup.2 in terms of solid content.
[0044] When the coating agent of the present invention is used as a
clear coating agent, the type of the paper to be coated is not
particularly limited. Examples of the paper include paper boards
such as manila board, white board, and liner; and printing paper
such as general high-quality paper, medium-quality paper, and
gravure paper.
[0045] Similarly, when the coating agent of the present invention
is used as a color developer coating agent, the type of the paper
to be coated is not particularly limited. Examples of the paper
include thermal paper, ink-jet printing paper, pressure-sensitive
paper, art coated paper, and lightweight coated paper.
[0046] When the coating agent of the present invention is used as a
clear coating agent, the coating agent is merely applied to the
paper surface of the paper to be coated.
[0047] When the coating agent of the present invention is used as a
color developer coating agent, a coating solution obtained by
mixing the coating agent with a color developer is applied to the
paper surface of the paper to be coated. The mixing ratio between
the coating agent and the color developer is not particularly
limited. Preferably, 0.5 to 15 parts by weight of the coating agent
is mixed with 100 parts by weight of the color developer, and more
preferably, 1 to 10 parts by weight of the coating agent is mixed
therewith. The solid content concentration of the coating solution
can be adjusted suitably in the range of 30 to 65 wt %.
[0048] Examples of the color developer to be mixed with the coating
agent include pigments such as clay, kaolin, calcium carbonate,
titanium white, and satin white.
[0049] The method of coating a paper surface with the coating agent
of the present invention is not particularly limited. A known
coater (a size press coater, an air knife coater, a blade coater,
or a roll coater) may be used. After coating of the paper surface,
optional processes such as a drying process and a calender process
may be carried out as required. Thus, the paper (thermal paper) of
the present invention can be obtained.
EXAMPLES
[0050] Hereinafter, the present invention is described further in
detail using examples. The present invention is not limited to the
examples described below. The units "part" and "%" indicated in the
examples are on the basis of weight unless otherwise specified.
Synthesis of Addition Condensate Between Ethylene Urea and
Glyoxal
Synthesis Example 1
[0051] In a four-necked flask equipped with a reflux condenser, a
thermometer, and a stirrer device, 86 parts of ethylene urea was
placed, and 129 parts of water and 130.5 parts of solution of
glyoxal with a concentration of 40% (equivalent to "ethylene
urea:glyoxal=1:0.9" in terms of molar ratio) were added thereto.
After pH of the system was adjusted to 7 using a solution of sodium
hydroxide with a concentration of 10% as a pH adjuster, ethylene
urea and glyoxal were allowed to react with each other at
60.degree. C. for ten hours. After completion of the reaction, it
was matured at 35.degree. C. for 16 hours. Thereafter, the
temperature of the system was lowered to 30.degree. C. or lower and
the pH of the system was adjusted to 6 using a solution of sulfuric
acid with a concentration of 20%. Thus, a pale yellow transparent
solution containing an addition condensate between ethylene urea
and glyoxal was obtained. In this case, the addition condensate in
the solution had a solid content concentration of 40%.
[0052] The average molecular weight of the addition condensate
obtained as described above, the content of the terminal aldehyde
groups in the addition condensate, and the amount of residual
glyoxal in the solution were evaluated by the following methods. As
a result, the average molecular weight (weight average molecular
weight) was approximately 720, the content of the terminal aldehyde
groups was 1.81 (mmol/g-solid content), and the amount of residual
glyoxal was 0.1 wt %. The methods of evaluating these values are
the same in the following synthesis examples.
<Evaluation of Average Molecular Weight of Addition
Condensate>
[0053] The average molecular weight of the addition condensate was
determined by gel permeation chromatography (GPC). The conditions
for the analysis were as follows.
[0054] Standard substance: polyethylene glycol, analyzer: LC-6A
(manufactured by Shimadzu Corporation), column: HSP gel AQ2.5
(manufactured by Waters), column size: 6.0.times.150 mm, column
temperature: 20.degree. C., detector: RID-6A (manufactured by
Shimadzu Corporation), elute: distilled water (manufactured by Wako
Pure Chemical Industries, Ltd.), flow rate: 0.3 ml/min, injected
sample concentration: 0.4 mg/mL, and the amount of injected sample:
5 .mu.L.
<Evaluation of the Amount of Residual Glyoxal in
Solution>
[0055] The amount of residual glyoxal in the above-mentioned
solution was determined by a high-performance liquid chromatography
method. The conditions for the analysis were as follows.
[0056] Analyzer: LC-6A (manufactured by Shimadzu Corporation),
column: Shim-pack CLC-ODS (manufactured by Shimadzu Corporation),
column size: 6.0.times.150 mm, column temperature: 40.degree. C.,
detector: RID-6A (manufactured by Shimadzu Corporation), elute:
distilled water (manufactured by Wako Pure Chemical Industries,
Ltd.), flow rate: 0.3 ml/min, injected sample concentration: 4.0
mg/mL, and the amount of injected sample: 5 .mu.L.
<Evaluation of the Content of Terminal Aldehyde Groups in
Addition Condensate>
[0057] With reference to Bunseki Kagaku Benran (edited by The Japan
Society for Analytical Chemistry, revised third edition, p. 314),
the amount (wt %) of all aldehyde groups that are present in the
aforementioned solution was determined by an acidic sodium sulfite
process, and the amount (wt %) of the residual glyoxal determined
as described above, which is indicated in terms of aldehyde groups,
was subtracted from the amount of all aldehyde groups determined
above. The value thus obtained was divided by the solid content
concentration (wt %) of the addition condensate and the molecular
weight (Mw=29) of the aldehyde groups. The value thus obtained was
taken as the content (mmol/g-solid content) of the terminal
aldehyde groups in the addition condensate.
[0058] The specific procedure of the acidic sodium sulfite process
(direct process) is described below. One gram of sample, 5 mL of
aqueous solution of sodium sulfite (NaHSO.sub.3) with a
concentration of 0.3 M, and 5 mL of water were mixed together. The
mixture thus obtained was sealed and was allowed to stand for one
hour. Subsequently, 0.5 mL of starch indicator was added to the
mixture, which was then titrated immediately with a 0.1N I.sub.2
solution. Then the amount (wt %) of all aldehyde groups that are
present in the aforementioned solution can be determined from the
amount A (mL) of the I.sub.2 solution required for the titration by
the following formula:
The amount of all aldehyde groups (wt
%)=(A.times.0.1.times.29)/(2.times.1000).times.100 (%)
Synthesis Example 2
[0059] A pale yellow transparent solution containing an addition
condensate between ethylene urea and glyoxal was obtained in the
same manner as in Synthesis Example 1 except that 174 parts of
solution of glyoxal with a concentration of 40% (equivalent to
"ethylene urea:glyoxal=1:1.2" in terms of molar ratio) was used.
The addition condensate in this solution had a solid content
concentration of 40%.
[0060] The average molecular weight of the addition condensate
obtained as described above, the content of the terminal aldehyde
groups in the addition condensate, and the amount of the residual
glyoxal in the solution were evaluated. As a result, the average
molecular weight (weight average molecular weight) was
approximately 820, the content of the terminal aldehyde groups was
2.16 (mmol/g-solid content), and the amount of the residual glyoxal
was 0.3 wt %.
Synthesis Example 3
[0061] A pale yellow transparent solution containing an addition
condensate between ethylene urea and glyoxal was obtained in the
same manner as in Synthesis Example 1 except that 188.5 parts of
solution of glyoxal with a concentration of 40% (equivalent to
"ethylene urea:glyoxal=1:1.3" in terms of molar ratio) was used.
The addition condensate in this solution had a solid content
concentration of 40%.
[0062] The average molecular weight of the addition condensate
obtained as described above, the content of the terminal aldehyde
groups in the addition condensate, and the amount of the residual
glyoxal in the solution were evaluated. As a result, the average
molecular weight (weight average molecular weight) was
approximately 880, the content of the terminal aldehyde groups was
2.41 (mmol/g-solid content), and the amount of the residual glyoxal
was 0.5 wt %.
Synthesis Example 4
[0063] In a four-necked flask similar to that used in Synthesis
Example 1, 86 parts of ethylene urea was placed, and 129 parts of
water and 111.7 parts of solution of glyoxal with a concentration
of 40% (equivalent to "ethylene urea:glyoxal=1:0.77" in terms of
molar ratio) were then added thereto. After pH of the system was
adjusted to 7.5 using a solution of sodium hydroxide with a
concentration of 10% as a pH adjuster, this was stirred at
55.degree. C. for one hour. Subsequently, after the pH of the
system was adjusted to 6.5 using sulfuric acid with a concentration
of 20% as a pH adjuster, ethylene urea and glyoxal were allowed to
react with each other at 55.degree. C. for 1.5 hours. After
completion of the reaction, the temperature of the system was
lowered to 30.degree. C. or lower and the pH of the system was
adjusted to 7 using a solution of sodium hydroxide with a
concentration of 25%. Thereafter, water was added thereto so that a
solid content concentration of 40% was obtained. Thus, a pale
yellow transparent solution containing an addition condensate
between ethylene urea and glyoxal was obtained.
[0064] The average molecular weight of the addition condensate
obtained as described above, the content of the terminal aldehyde
groups in the addition condensate, and the amount of the residual
glyoxal in the solution were evaluated. As a result, the average
molecular weight (weight average molecular weight) was
approximately 650, the content of the terminal aldehyde groups was
0.78 (mmol/g-solid content), and the amount of the residual glyoxal
was not detected.
Synthesis Example 5
[0065] A pale yellow transparent solution containing an addition
condensate between ethylene urea and glyoxal was obtained in the
same manner as in Synthesis Example 4 except that 116.0 parts of
solution of glyoxal with a concentration of 40% (equivalent to
"ethylene urea:glyoxal=1:0.8" in terms of molar ratio) was used.
The addition condensate in this solution had a solid content
concentration of 40%.
[0066] The average molecular weight of the addition condensate
obtained as described above, the content of the terminal aldehyde
groups in the addition condensate, and the amount of the residual
glyoxal in the solution were evaluated. As a result, the average
molecular weight (weight average molecular weight) was
approximately 700, the content of the terminal aldehyde groups was
1.21 (mmol/g-solid content), and the amount of the residual glyoxal
was not detected.
Synthesis Example 6
[0067] A pale yellow transparent solution containing an addition
condensate between ethylene urea and glyoxal was obtained in the
same manner as in Synthesis Example 1 except that 290.0 parts of
solution of glyoxal with a concentration of 40% (equivalent to
"ethylene urea:glyoxal=1:2.0" in terms of molar ratio) was used.
The addition condensate in this solution had a solid content
concentration of 40%.
[0068] The average molecular weight of the addition condensate
obtained as described above, the content of the terminal aldehyde
groups in the addition condensate, and the amount of the residual
glyoxal in the solution were evaluated. As a result, the average
molecular weight (weight average molecular weight) was
approximately 1150, the content of the terminal aldehyde groups was
3.71 (mmol/g-solid content), and the amount of the residual glyoxal
was 0.4 wt %.
[0069] The contents of the terminal aldehyde groups and the amounts
of the residual glyoxal in Synthesis Examples 1 to 6 are indicated
in Table 1 below together with the mixing ratios of ethylene urea
and glyoxal.
TABLE-US-00001 TABLE 1 Mixing Ratio (Molar Ratio) Content of
Terminal Amount of Ethylene Urea/ Aldehyde Groups Residual Glyoxal
Glyoxal (mmol/g solid content) (wt %) Synthesis 1/0.9 1.81 0.1
Example 1 Synthesis 1/1.2 2.16 0.3 Example 2 Synthesis 1/1.3 2.41
0.5 Example 3 Synthesis 1/0.77 0.78 Not detected Example 4
Synthesis 1/0.8 1.21 Not detected Example 5 Synthesis 1/2.0 3.71
0.4 Example 6
[Synthesis of PVA]
<PVA-1>
[0070] In a pressurized reaction vessel with an internal volume of
250 L that is provided with a stirrer, a nitrogen feed port, an
ethylene feed port, a port for adding a polymerization initiator,
and a port for adding a delay solution, 130.5 kg of vinyl acetate
monomers and 19.5 kg of methanol were placed. After the temperature
inside the vessel was increased to 60.degree. C., the inside of the
reaction system was subjected to nitrogen substitution by nitrogen
bubbling carried out for 30 minutes. Subsequently, ethylene gas was
introduced into the vessel so that the pressure inside the reaction
vessel reached 0.39 MPa. Thereafter, 90 mL of methanol solution of
AMV (2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile)) (with a
concentration of 2.8 g/L, which had been subjected to nitrogen
substitution by nitrogen bubbling) was added, as a polymerization
initiator, to the mixture of vinyl acetate monomers and methanol
inside the reaction vessel, and thereby copolymerization between
vinyl acetate monomers and ethylene was initiated. During the
polymerization, the temperature inside the vessel was maintained at
60.degree. C. and the above-mentioned AMV solution was fed
continuously, as a polymerization initiator, into the vessel at a
rate of 135 mL/h.
[0071] Approximately 4 hours later when the polymerization rate
reached 40%, the reaction system was cooled and thereby the
polymerization reaction was stopped. During the polymerization, the
pressure inside the vessel decreased gradually, and the pressure
was 0.37 MPa when the polymerization was stopped.
[0072] Next, the reaction vessel was opened and ethylene was
removed from the inside of the vessel. Thereafter, the inside of
the reaction system was subjected to deethylenation by nitrogen
bubbling. Subsequently, methanol vapor was introduced into the
reaction vessel, and unreacted vinyl acetate monomers remaining
inside the reaction system were discharged. Thus, a methanol
solution of polyvinyl acetate (ethylene-modified polyvinyl acetate)
(with a concentration of 40%) containing an ethylene unit as a
constituent unit was obtained.
[0073] Next, methanol was added to the resultant solution to adjust
it so that the polyvinyl acetate in the solution had a
concentration of 30%. Thereafter, 23.7 g of alkaline solution (a
methanol solution of sodium hydroxide with a concentration of 10%)
was added to 1000 g of the solution thus adjusted (containing 300 g
of the above-mentioned polyvinyl acetate) (the molar ratio of
sodium hydroxide to a vinyl acetate unit was 0.017), and thereby
ethylene-modified polyvinyl acetate was saponified. In this case,
the saponification was carried out at a temperature of 40.degree.
C.
[0074] The whole solution was gelled in approximately two minutes
after addition of the alkaline solution. The gel thus formed was
removed from the reaction vessel and was ground with a grinder.
This was allowed to stand at 40.degree. C. for one hour to further
be saponified. Thereafter, residual sodium hydroxide was
neutralized with methyl acetate. After the completion of
neutralization was checked with a phenolphthalein indicator, a
white solid obtained through filtering out was put into methanol
whose amount was five times the amount of the white solid to be
washed. This was allowed to stand at room temperature for three
hours. Subsequently, the washing operation including filtering out
and putting the white solid obtained through the filtering out into
methanol was repeated three times. Thereafter, the white solid
obtained by centrifugation was allowed to stand in a dryer kept at
70.degree. C. for one day to be dried. Thus, an ethylene-modified
PVA (PVA-1) was obtained. The degree of polymerization, the content
X of vinyl alcohol units (mol %), and the content Y of ethylene
units (mol %) in the PVA-lwere evaluated based on the provision of
JIS K6726 (The test methods for polyvinyl alcohol) and the
aforementioned method using .sup.1H-NMR. As a result, the degree of
polymerization was 1500, the content X was 97.5 mol %, and the
content Y was 3.0 mol %.
<PVA-2 to PVA-17>
[0075] The conditions for polymerizing vinyl acetate monomers
and/or the conditions for saponification were varied, and thereby
16 types of PVAs (PVA-2 to PVA-17) were obtained that were
different from the PVA-1 in at least one selected from the degree
of polymerization, the content X, and the content Y. The degree of
polymerization, the content X, and the content Y in each of the
PVAs synthesized above including the PVA-1 are indicated together
in Table 2 below. The PVA-11 to PVA-13 were produced by allowing
the polymerization reaction to proceed without introducing ethylene
gas into the reaction vessel.
TABLE-US-00002 TABLE 2 Content X of Content Y of Degree of Vinyl
Alcohol Ethylene Polymerization Units (mol %) Units (mol %) X +
0.2Y PVA-1 1500 97.5 3.0 98.1 PVA-2 98.5 99.1 PVA-3 99.5 100.1
PVA-4 99.3 5.0 100.3 PVA-5 98.5 99.5 PVA-6 97.0 98.0 PVA-7 94.5
95.5 PVA-8 500 98.5 9.0 100.3 PVA-9 96.5 98.3 PVA-10 94.0 95.8
PVA-11 1750 99.5 0 99.5 PVA-12 98.5 98.5 PVA-13 94.5 94.5 PVA-14
1500 94.0 3.0 94.6 PVA-15 93.5 5.0 94.5 PVA-16 99.9 100.9 PVA-17
500 92.5 9.0 94.3
Production of Coating Agent
Example 1
[0076] Ninety grams of aluminum hydroxide powder (HIGILITE H42,
manufactured by Showa Denko K.K.) was put into 210 g of distilled
water, which was then stirred manually. Thereafter, this was
stirred with a homomixer (T-25-SI, manufactured by
IKA-Labortechnik) at a rotation speed of 13500 rpm for five
minutes. Thus, an aluminum hydroxide dispersion solution A (with an
aluminum hydroxide concentration of 30%) was prepared.
[0077] Separately, the PVA-1 was dissolved in hot water at
95.degree. C., and thereby a aqueous solution of PVA with a
concentration of 10% was prepared.
[0078] Next, 60 g of the PVA aqueous solution was added to 22 g of
the dispersion solution A. After they were mixed together
homogeneously, further Synthesis Example 1 was added thereto as an
addition condensate in such a manner that the ratio of PVA:addition
condensate (solid content weight ratio) was 90:10, which was then
mixed together homogeneously. Thereafter, distilled water was added
thereto so that a solid content concentration of 15% was obtained.
Thus, a coating agent (Example 1) was obtained. The viscosity of
the coating agent thus obtained was measured with a B-type
viscometer at a temperature of 20.degree. C., with the rotation
speed of the inner cylinder being 60 rpm, and was determined to be
480 mPas.
[0079] The viscosity stability of the coating agent obtained above
was evaluated by the following method. The evaluation results are
indicated in Table 3 below.
[Viscosity Stability]
[0080] The coating agent obtained as described above was allowed to
stand at a temperature of 20.degree. C. for 20 hours and then the
viscosity thereof after standing was measured with the B-type
viscometer in the same manner as described above. The ratio of the
viscosity to the initial viscosity was determined as a viscosity
increase ratio (=viscosity after standing/initial viscosity). The
viscosity stability of the coating agent was evaluated on a 3-point
scale described below, based on the value of the viscosity increase
ratio determined above.
--Criteria for Judging Viscosity Stability--
[0081] .smallcircle. (Good): The viscosity increase ratio was lower
than 1.5. .DELTA. (Acceptable): The viscosity increase ratio was
1.5 or higher but lower than 3.0. x (Unacceptable): The viscosity
increase ratio was 3.0 or higher.
[0082] Next, the coating agent obtained as described above was
applied manually onto a paper surface of commercial thermal paper
(manufactured by Kokuyo Co., Ltd.) with a wire bar No. 14
(manufactured by ETO). Thereafter, the coated surface was dried
with a hot air dryer at 50.degree. C. for five hours. Subsequently,
the thermal paper thus dried was allowed to stand for three hours
in a room adjusted to 20.degree. C. and 65% RH. This was used as a
sample for evaluating the properties (water resistance, blocking
resistance, plasticizer resistance, and the degree of yellowing
over time) of the layer formed of the coating agent.
[Water Resistance]
[0083] After the above-mentioned sample was immersed in water at
40.degree. C. for 24 hours, the coated surface was rubbed with a
finger ten times and the state of peeling produced at the surface
was then observed. The water resistance of the layer formed of the
coating agent was evaluated on a 5-point scale by judging the state
thus observed according to the following criteria.
--Criteria for Judging Water Resistance--
[0084] 5: No peeling of the surface was observed. 4: A very little
peeling of the surface was observed. 3: A little peeling of the
surface was observed. 2: Much peeling of the surface was observed.
1: Most part of the surface was peeled.
[Blocking Resistance (Surface Water Resistance)]
[0085] The above-mentioned sample was allowed to stand in an
atmosphere with a temperature of 40.degree. C. for 72 hours and was
then cut into five centimeters square pieces. Subsequently, a drop
(about 30 .mu.L) of water was dropped on the coated surface.
Thereafter, another sample on which no waterdrop was dropped was
then placed thereon so that the coated surfaces of both were in
contact with each other, which was then subjected to natural
drying. After drying, the samples were separated from each other
and their conditions after separation were observed. The blocking
resistance of the layer formed of the coating agent was evaluated
on a 3-point scale by judging the condition thus observed according
to the following criteria.
--Criteria for Judging Blocking Resistance--
[0086] 3: Samples were separated spontaneously without any force
being applied. 2: Surfaces adhered partially to each other but no
tears were caused in the samples. 1: Surfaces adhered to each other
and the samples were torn upon separation
[Plasticizer Resistance]
[0087] Printing was carried out with a commercial thermal paper
facsimile (RIFAX 300, manufactured by Ricoh Company, Ltd.), with
the coated surface of the above-mentioned sample being used as a
printing surface. Subsequently, a wrap film (HI-WRAP SAS,
manufactured by Mitsui Chemicals, Inc.) was wound three times
around a polycarbonate pipe (with a diameter of 40 mm), and the
above-mentioned printed sample was then wound thereon. Thereafter,
further the above-mentioned wrap film was wound three times
thereon. This was then allowed to stand in an atmosphere with a
temperature of 40.degree. C. for 24 hours, and the printing density
after standing was measured with a Macbeth densitometer. Thus, the
plasticizer resistance of the layer formed of the coating agent was
evaluated. Larger numerical values indicated in Table 3 denote that
the printing density was maintained, that is, the plasticizer
resistance of the layer formed of the coating agent is high.
[The Degree of Yellowing Over Time]
[0088] Printing was carried out with the above-mentioned thermal
paper facsimile, with the coated surface of the above-mentioned
sample being used as a printing surface. Subsequently, the printed
sample was allowed to stand in a thermo-hygrostat adjusted to
40.degree. C. and 95% RH for three weeks. The color tone of the
sample after standing was measured with a colorimeter (PF-10,
manufactured by NDK, Incorporated), and the b-value was evaluated
as a measure that indicates the yellow tinge thereof. Larger
numerical values of the b-value denote stronger degrees of yellow,
that is, advanced yellowing.
Examples 2 to 20 and Comparative Examples 1 to 10
[0089] The addition condensates formed as Synthesis Examples 1 to 6
and PVA-1 to PVA-17 were mixed together at the ratios indicated in
Tables 3A and 3B below in the same manner as in Example 1, and
thereby coating agents (Examples 2 to 20 and Comparative Examples 1
to 10) were obtained. In Comparative Example 8, glyoxal was used as
a crosslinker instead of the addition condensate.
[0090] The viscosity stability of the coating agents thus obtained
and properties of the layers formed of the coating agents were
evaluated in the same manner as in Example 1. The evaluation
results are indicated in Tables 3A and 3B below.
TABLE-US-00003 TABLE 3A Composition of Coating Agent Properties of
Mixing Ratio of PVA Coating Agent and Addition Condensate Initial
Properties of Layer formed of Coating Agent (Solid Content Weight
Ratio) Viscosity Viscosity Water Blocking Plasticizer PVA Addition
Condensate PVA: Addition Condensate (mPa s) Stability Resistance
Resistance Resistance b-value Example 1 PVA-1 Synthesis Example 1
90:10 480 .smallcircle. 4 3 1.4 2.8 Example 2 Synthesis Example 2
480 .smallcircle. 4 3 1.4 2.8 Example 3 Synthesis Example 3 480
.smallcircle. 4 3 1.4 3.5 Example 4 Synthesis Example 5 480
.smallcircle. 3 3 1.4 2.8 Example 5 PVA-2 Synthesis Example 1 480
.smallcircle. 4 3 1.4 2.8 Example 6 PVA-3 480 .smallcircle. 5 3 1.4
2.8 Example 7 PVA-4 480 .smallcircle. 5 3 1.4 2.8 Example 8
Synthesis Example 2 480 .smallcircle. 5 3 1.4 2.8 Example 9
Synthesis Example 3 480 .smallcircle. 5 3 1.4 3.5 Example 10 PVA-5
Synthesis Example 1 480 .smallcircle. 3 2 1.4 2.8 Example 11 PVA-6
480 .smallcircle. 3 2 1.4 2.8 Example 12 PVA-7 480 .smallcircle. 3
2 1.4 2.8 Example 13 PVA-8 230 .DELTA. 5 3 1.2 2.8 Example 14
Synthesis Example 2 230 .smallcircle. 5 3 1.2 2.8 Example 15
Synthesis Example 3 230 .smallcircle. 5 3 1.2 3.5 Example 16 PVA-9
Synthesis Example 1 230 .DELTA. 3 2 1.2 2.8 Example 17 PVA-10 230
.DELTA. 3 2 1.2 2.8 Example 18 PVA-11 480 .smallcircle. 3 2 1.4 2.8
Example 19 PVA-12 480 .smallcircle. 3 2 1.4 2.8 Example 20 PVA-1
60:40 830 .DELTA. 4 3 1.4 3
TABLE-US-00004 TABLE 3B Composition of Coating Agent Mixing Ratio
of PVA Properties of Coating Agent and Addition Condensate Initial
Properties of Layer formed of Coating Agent Addition (Solid Content
Weight Ratio) Viscosity Viscosity Water Blocking Plasticizer PVA
Condensate PVA: Addition Condensate (mPa s) Stability Resistance
Resistance Resistance b-value Comparative PVA-13 Synthesis 90:10
450 .smallcircle. 1 1 1.4 2.8 Example 1 Example 1 Comparative
PVA-14 480 .smallcircle. 1 1 1.4 2.8 Example 2 Comparative PVA-15
480 .smallcircle. 1 1 1.4 2.8 Example 3 Comparative PVA-16 620 x 5
3 1.4 2.8 Example 4 Comparative PVA-17 220 x 1 1 1.2 2.8 Example 5
Comparative PVA-1 Synthesis 480 .smallcircle. 1 1 1.4 2.8 Example 6
Example 4 Comparative Synthesis 480 x 5 3 1.4 4.1 Example 7 Example
6 Comparative Glyoxal -- 480 .smallcircle. 1 2 1.4 5.1 Example 8
Comparative Synthesis 99.5:0.5 460 .smallcircle. 2 1 1.4 2.8
Example 9 Example 1 Comparative 40:60 1080 x 4 3 1.4 3.4 Example
10
[0091] As indicated in Tables 3A and 3B, in Examples 1 to 20 of the
coating agents of the present invention, the viscosity stability
thereof and various properties of the layers formed using the
coating agents were expressed in a well balanced manner at a high
level.
[0092] Among Examples 1 to 20, Examples 6 to 9 and 13 to 15 in
which the value of "X+0.2Y" exceeded 100 made it possible to form
layers having further higher water resistance.
[0093] On the other hand, the values of "X+0.2Y" in Comparative
Examples 1 to 3 and 5, the content X of vinyl alcohol units in
Comparative Example 4, the contents of the terminal aldehyde groups
in the addition condensates in Comparative Examples 6 and 7, and
the mixing ratios of PVA and addition condensate in Comparative
Examples 9 and 10 were out of the ranges specified in the present
invention and the above-mentioned properties were not expressed in
a well balanced manner. More specifically, they were poor in water
resistance and blocking resistance or were subjected to
deterioration in the viscosity stability of the coating agent.
Furthermore, in Comparative Example 7 using the addition condensate
(Synthesis Example 6) in which the content of the terminal aldehyde
groups was larger than the range specified in the present
invention, the degree of yellowing over time increased in addition
thereto.
[0094] Moreover, in Comparative Example 8 in which glyoxal was used
as a crosslinker, it was poor in water resistance and the degree of
yellowing over time increased significantly.
[0095] The present invention is applicable to other embodiments as
long as they do not depart from the spirit and essential
characteristics thereof. The embodiments disclosed in this
specification are to be considered in all respects as illustrative
and not limiting. The scope of the present invention is indicated
by the appended claims rather than by the foregoing description,
and all changes that come within the meaning and range of
equivalency of the claims are intended to be embraced therein.
INDUSTRIAL APPLICABILITY
[0096] As described above, the use of a coating agent for paper of
the present invention allows a curing step to be omitted after a
paper surface is coated therewith and makes it possible to form a
layer (for example, a coating layer or a color developing layer)
that is excellent in water resistance and is subjected to less
yellowing over time. That is, paper having a layer (for example, a
coating layer or a color developing layer) that is excellent in
water resistance and is subjected to less yellowing over time can
be produced, and the paper is excellent in, for example, water
resistance, image record retention properties, plasticizer
resistance, and productivity and can be used suitably for various
printing methods including offset printing and thermal
printing.
* * * * *